TOPIC
about_For
SHORT DESCRIPTION
Describes a language command you can use to run statements based on a
conditional test.
LONG DESCRIPTION
The For statement (also known as a For loop) is a language construct
you can use to create a loop that runs commands in a command block while a
specified condition evaluates to true.
A typical use of the For loop is to iterate an array of values and to
operate on a subset of these values. In most cases, if you want to
iterate all the values in an array, consider using a Foreach statement.
Syntax
The following shows the For statement syntax.
for (<init>; <condition>; <repeat>)
{<statement list>}
The <init> placeholder represents one or more commands, separated by
commas, that are run before the loop begins. You typically use the
<init> portion of the statement to create and initialize a variable with
a starting value.
This variable will then be the basis for the condition to be tested in
the next portion of the For statement.
The <condition> placeholder represents the portion of the For statement
that resolves to a true or false Boolean value. Windows PowerShell
evaluates the condition each time the For loop runs. If the statement is
true, the commands in the command block run, and the statement is
evaluated again. If the condition is still true, the commands in the
statement list run again. The loop is repeated until the condition
becomes false.
The <repeat> placeholder represents one or more commands, separated by
commas, that are executed each time the loop repeats. Typically, this
is used to modify a variable that is tested inside the <condition> part
of the statement.
The <statement list> placeholder represents a set of one or more commands
that are run each time the loop is entered or repeated. The contents of
the statement list are surrounded by braces.
Examples
At a minimum, a For statement requires the parenthesis surrounding the
<init>, <condition>, and <repeat> part of the statement and a command
surrounded by braces in the <statement list> part of the statement.
Note that the upcoming examples intentionally show code outside the
For statement. In later examples, code is integrated into the for
statement.
For example, the following For statement continually displays the
value of the $i variable until you manually break out of the command by
pressing CTRL+C.
$i = 1
for (;;){Write-Host $i}
You can add additional commands to the statement list so that
the value of $i is incremented by 1 each time the loop is run, as the
following example shows.
for (;;){$i++; Write-Host $i}
Until you break out of the command by pressing CTRL+C, this statement
will continually display the value of the $i variable as it is
incremented by 1 each time the loop is run.
Rather than change the value of the variable in the statement list
part of the For statement, you can use the <repeat> portion of the For
statement instead, as follows.
$i=1
for (;;$i++){Write-Host $i}
This statement will still repeat indefinitely until you break out of the
command by pressing CTRL+C.
By setting a condition (using the <condition> portion of the For
statement), you can end the For loop when the condition evaluates to
false. In the following example, the For loop runs while the value of
$i is less than or equal to 10.
$i=1
for(;$i -le 10;$i++){Write-Host $i}
Instead of creating and initializing the variable outside the For
statement, you can perform this task inside the For loop by using
the <init> portion of the For statement.
for($i=1; $i -le 10; $i++){Write-Host $i}
You can use carriage returns instead of semicolons to delimit the
<init>, <condition>, and <repeat> portions of the For statement. The
following example shows the For statement syntax in this alternative
form.
for (<init>
<condition>
<repeat>){
<statement list>
}
This alternative form of the For statement works in Windows PowerShell
script files and at the Windows PowerShell command prompt. However, it
is easier to use the For statement syntax with semicolons when you enter
interactive commands at the command prompt.
The For loop is more flexible than the Foreach loop because it allows
you to increment values in an array or collection by using patterns. In
the following example, the $i variable is incremented by 2 in the
<repeat> portion of the for statement.
for ($i = 0; $i -ile 20; $i += 2) {Write-Host $i}
SEE ALSO
about_Comparison_Operators
about_Foreach